Create your first durable function in JavaScript

Durable Functions is an extension of Azure Functions that lets you write stateful functions in a serverless environment. The extension manages state, checkpoints, and restarts for you.

In this article, you learn how to use the Visual Studio Code Azure Functions extension to locally create and test a "hello world" durable function. This function will orchestrate and chain together calls to other functions. You then publish the function code to Azure.

Running durable function in Azure

Prerequisites

To complete this tutorial:

If you don't have an Azure subscription, create a free account before you begin.

Create your local project

In this section, you use Visual Studio Code to create a local Azure Functions project.

  1. In Visual Studio Code, press F1 (or Ctrl/Cmd+Shift+P) to open the command palette. In the command palette, search for and select Azure Functions: Create New Project....

    Create function

  2. Choose an empty folder location for your project and choose Select.

  3. Following the prompts, provide the following information:

    Prompt Value Description
    Select a language for your function app project JavaScript Create a local Node.js Functions project.
    Select a version Azure Functions v3 You only see this option when the Core Tools aren't already installed. In this case, Core Tools are installed the first time you run the app.
    Select a template for your project's first function Skip for now
    Select how you would like to open your project Open in current window Reopens VS Code in the folder you selected.

Visual Studio Code installs the Azure Functions Core Tools, if needed. It also creates a function app project in a folder. This project contains the host.json and local.settings.json configuration files.

A package.json file is also created in the root folder.

Enable compatibility mode

Currently, JavaScript Durable Functions require Azure Functions V2 compatibility mode to be enabled.

  1. Open local.settings.json to edit the settings used when running the app locally.

  2. Add a setting named FUNCTIONS_V2_COMPATIBILITY_MODE with a value of true.

    {
        "IsEncrypted": false,
        "Values": {
            "AzureWebJobsStorage": "",
            "FUNCTIONS_WORKER_RUNTIME": "node",
            "FUNCTIONS_V2_COMPATIBILITY_MODE": "true"
        }
    }
    

Install the Durable Functions npm package

To work with Durable Functions in a Node.js function app, you use a library called durable-functions.

  1. Use the View menu or Ctrl+Shift+` to open a new terminal in VS Code.

  2. Install the durable-functions npm package by running npm install durable-functions in the root directory of the function app.

Creating your functions

The most basic Durable Functions app contains three functions:

  • Orchestrator function - describes a workflow that orchestrates other functions.
  • Activity function - called by the orchestrator function, performs work, and optionally returns a value.
  • Client function - a regular Azure Function that starts an orchestrator function. This example uses an HTTP triggered function.

Orchestrator function

You use a template to create the durable function code in your project.

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions orchestrator Create a Durable Functions orchestration
    Provide a function name HelloOrchestrator Name of your durable function

You've added an orchestrator to coordinate activity functions. Open HelloOrchestrator/index.js to see the orchestrator function. Each call to context.df.callActivity invokes an activity function named Hello.

Next, you'll add the referenced Hello activity function.

Activity function

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions activity Create an activity function
    Provide a function name Hello Name of your activity function

You've added the Hello activity function that is invoked by the orchestrator. Open Hello/index.js to see that it's taking a name as input and returning a greeting. An activity function is where you'll perform actions such as making a database call or performing a computation.

Finally, you'll add an HTTP triggered function that starts the orchestration.

Client function (HTTP starter)

  1. In the command palette, search for and select Azure Functions: Create Function....

  2. Following the prompts, provide the following information:

    Prompt Value Description
    Select a template for your function Durable Functions HTTP starter Create an HTTP starter function
    Provide a function name DurableFunctionsHttpStart Name of your activity function
    Authorization level Anonymous For demo purposes, allow the function to be called without authentication

You've added an HTTP triggered function that starts an orchestration. Open DurableFunctionsHttpStart/index.js to see that it uses client.startNew to start a new orchestration. Then it uses client.createCheckStatusResponse to return an HTTP response containing URLs that can be used to monitor and manage the new orchestration.

You now have a Durable Functions app that can be run locally and deployed to Azure.

Test the function locally

Azure Functions Core Tools lets you run an Azure Functions project on your local development computer. You're prompted to install these tools the first time you start a function from Visual Studio Code.

  1. To test your function, set a breakpoint in the Hello activity function code (Hello/index.js). Press F5 or select Debug: Start Debugging from the command palette to start the function app project. Output from Core Tools is displayed in the Terminal panel.

    Note

    Refer to the Durable Functions Diagnostics for more information on debugging.

  2. Durable Functions requires an Azure Storage account to run. When VS Code prompts you to select a storage account, choose Select storage account.

    Create storage account

  3. Following the prompts, provide the following information to create a new storage account in Azure.

    Prompt Value Description
    Select subscription name of your subscription Select your Azure subscription
    Select a storage account Create a new storage account
    Enter the name of the new storage account unique name Name of the storage account to create
    Select a resource group unique name Name of the resource group to create
    Select a location region Select a region close to you
  4. In the Terminal panel, copy the URL endpoint of your HTTP-triggered function.

    Azure local output

  5. Using a tool like Postman or cURL, send an HTTP POST request to the URL endpoint. Replace the last segment with the name of the orchestrator function (HelloOrchestrator). The URL should be similar to http://localhost:7071/api/orchestrators/HelloOrchestrator.

    The response is the initial result from the HTTP function letting you know the durable orchestration has started successfully. It is not yet the end result of the orchestration. The response includes a few useful URLs. For now, let's query the status of the orchestration.

  6. Copy the URL value for statusQueryGetUri and paste it in the browser's address bar and execute the request. Alternatively you can also continue to use Postman to issue the GET request.

    The request will query the orchestration instance for the status. You should get an eventual response, which shows us the instance has completed, and includes the outputs or results of the durable function. It looks like:

    {
        "name": "HelloOrchestrator",
        "instanceId": "9a528a9e926f4b46b7d3deaa134b7e8a",
        "runtimeStatus": "Completed",
        "input": null,
        "customStatus": null,
        "output": [
            "Hello Tokyo!",
            "Hello Seattle!",
            "Hello London!"
        ],
        "createdTime": "2020-03-18T21:54:49Z",
        "lastUpdatedTime": "2020-03-18T21:54:54Z"
    }
    
  7. To stop debugging, press Shift + F5 in VS Code.

After you've verified that the function runs correctly on your local computer, it's time to publish the project to Azure.

Sign in to Azure

Before you can publish your app, you must sign in to Azure.

  1. If you aren't already signed in, choose the Azure icon in the Activity bar, then in the Azure: Functions area, choose Sign in to Azure.... If you don't already have one, you can Create a free Azure account.

    Function localhost response in the browser

    If you're already signed in, go to the next section.

  2. When prompted in the browser, choose your Azure account and sign in using your Azure account credentials.

  3. After you've successfully signed in, you can close the new browser window. The subscriptions that belong to your Azure account are displayed in the Side bar.

Publish the project to Azure

In this section, you create a function app and related resources in your Azure subscription and then deploy your code.

Important

Publishing to an existing function app overwrites the content of that app in Azure.

  1. Choose the Azure icon in the Activity bar, then in the Azure: Functions area, choose the Deploy to function app... button.

    Publish your project to Azure

  2. Provide the following information at the prompts:

    • Select folder: Choose a folder from your workspace or browse to one that contains your function app. You won't see this if you already have a valid function app opened.

    • Select subscription: Choose the subscription to use. You won't see this if you only have one subscription.

    • Select Function App in Azure: Choose + Create new Function App. (Don't choose the Advanced option, which isn't covered in this article.)

    • Enter a globally unique name for the function app: Type a name that is valid in a URL path. The name you type is validated to make sure that it's unique in Azure Functions.

    • Select a runtime: Choose the version of Python you've been running on locally. You can use the python --version command to check your version.
    • Select a runtime: Choose the version of Node.js you've been running on locally. You can use the node --version command to check your version.
    • Select a location for new resources: For better performance, choose a region near you.
  3. When completed, the following Azure resources are created in your subscription, using names based on your function app name:

    • A resource group, which is a logical container for related resources.
    • A standard Azure Storage account, which maintains state and other information about your projects.
    • A consumption plan, which defines the underlying host for your serverless function app.
    • A function app, which provides the environment for executing your function code. A function app lets you group functions as a logical unit for easier management, deployment, and sharing of resources within the same hosting plan.
    • An Application Insights instance connected to the function app, which tracks usage of your serverless function.

    A notification is displayed after your function app is created and the deployment package is applied.

  4. Select View Output in this notification to view the creation and deployment results, including the Azure resources that you created. If you miss the notification, select the bell icon in the lower right corner to see it again.

    Create complete notification

Enable compatibility mode

The same Azure Functions V2 compatibility that you enabled locally needs to be enabled in the app in Azure.

  1. Using the command palette, search for and select Azure Functions: Edit Setting....

  2. Follow the prompts to locate your function app in your Azure subscription.

  3. Select Create new App Setting....

  4. Enter a new setting key of FUNCTIONS_V2_COMPATIBILITY_MODE.

  5. Enter a setting value of true.

Test your function in Azure

  1. Copy the URL of the HTTP trigger from the Output panel. The URL that calls your HTTP-triggered function should be in this format: http://<functionappname>.azurewebsites.net/orchestrators/HelloOrchestrator

  2. Paste this new URL for the HTTP request into your browser's address bar. You should get the same status response as before when using the published app.

Next steps

You have used Visual Studio Code to create and publish a JavaScript durable function app.